Stabilization of synthetic rubberlike materials



Patented Jan. 27, 1942 2,270,959 7 STABEIZATION or smna'nc nonsen- LIKEMATERIALS Hans Murke, Leverkusen-Scblebusch, and Wilhelm Becker,Cologne, Germany, assignors to I. G. Far-benindustrieAktiengesellscliaft, Frankfort-on-the-Main, Germany No Drawing.

Application September 27, 1939,

Serial No. 296,810. In Germany October 14,

3 Claims.

The present invention relates to a new process for stabilizing syntheticrubber-like materials prepared by the polymerization of butadienes-1.3'.

It is known that synthetic rubberlike materials of the characterdescribed are liable to a self-hardening. This is probably due to alinkme of the individual chains with the formation of cyclic compounds.In consequence of this cyclicisation the working of these products onthe roller is connected with considerable difllculties and expenses and,moreover, the mechanical properties of the vulcanizates obtainedtherefrom are impaired. Apart from this phenomenon, the polymerizates ofthe character described show the undesired property of being attacked bythe oxygen of the air.

Many attempts have been made to avoid these disadvantages by theaddition of stabilizing agents. To this end there have been incorporatedwithin the polymerizates of the character described aromatic secondaryamines, polyvalent aromatic hydroxy compounds and finally aldehyde-aminecondensation products. All products of this type though exerting somestabilizing eifect involve the disadvantage of impairing the stabilitytowards light. In consequence thereof, no clear success has been reachedup to the present time.

Other stabilizing agents, for instance those described and claimed inthe application Ser. No. 181,604 to Ingofroh Dennstedt and Harro Hagenand Wilhelm Becker filed December 24, 1937, though being free from theabove disadvantages show a disagreeable odor which may be such as toprevent their practical use.

It is the object of our present invention to develop new auxiliaryagents which show a good stabilizing action without impairing thefastness to light and are free from any objectionable odor thus allowingthe preparation of light-colored and non-smelling rubber materials.

Our new stabilizers'may be defined as products of the condensition ofaldehydes or ketones with phenols or naphthols, as far as such productsare still soluble in organic solvents. Stabilizers of the characterdescribed, if incorporated within polymerizates of butadienes-L3 priorto storing, meet every practical demand with respect to the stabilizingaction, with respect to fastness towards light of the vulcanizates andwith respect to the odor. As synthetic rubberlike materials which may bestabilized in accordance with the present invention there may bementioned the polymerizates of butadiene, isoprene, dimethylbutadienes,Z-chlorobutadiene, and finally the products of the conjointpolymerization of such butadienes with other polymerizable substancessuch as styrene or acrylic acid nitrile. The incorporation of thestabilizers within these synthetic rubber-like materials can be effectedin a solid state, for instance, on the roller. The simplest way is toadd the stabilizers either dissolved in alkalies or in form of anaqueous suspension, to the polymerizates obtained in form of a latexaccording to the emulsion polymerization.

The following details serve to more fully explain the nature and theefficacy of our new stabilizers. First of all, they must be capable ofbeing dissolved by organic solvents as insoluble products, owing totheir too high degree of condensation, would be unsuitable for thepurpose in question. The required properties can be easily regulated ina manner known per se by controlling the conditions of temperature andby a suitable choice of the starting materials and of the catalysts.Preference is given to those products having been prepared in an acidmedium and being soluble in alkalies, as such products can be mosteasily incorporated within the emulsion polymerizates, viz. in form ofen aqueous alkaline solution. Generally speaking, products of theso-called Novolak-type are most suitable for the purpose of ourinvention. Also the lowest members of the condensation, for instance,those which are composed of 2 mo1s of phenols and 1 mol of aldehyde, of3 mols of phenols and 2 mols of aldehydes and of 4 mols of phenols and 3mols of aldehydes, have proved to be efiective though, in practicalworking, mixtures of the various condensation products are employed, asthe isolation of the various uniform compounds from such mixtures isconnected with considerable diificulties. We wish to point out that incase of working with mixtures of the character described the excessunchanged phenol or naphthol should be removed' by distillation invacuo. In accordance with a preferred form of our invention we areworking with hydrogenated condensation products of the characterdescribed, 1. e. with such products as have been subjected to ahydrogenating treatment subsequent to condensation and, if desired, topurification. Amongst the hydrogenated products those must bechosenwhich have taken up at the most of the hydrogen necessary for effectingcomplete hydrogenation of the arcmatic nuclei contained therein, asbeyond this limit the capability of such products of protecting thesynthetic rubber against the attack of oxygen gradually disappears. Thehydrogenation of the condensation products can be performed byintroducing hydrogen into a solution thereof in an organic solvent suchas methylalcohol or tetrahydrofurane, at an elevat d temperature of sayabout 100 to 200 C. and a a high pressure of about 200 atmospheres. Thehydrogenation must be interrupted as soon as the desired stage has beenreached. The said hydrogenation serves to more completely exclude anyinconvenience regarding the odor which might be caused by traces ofunchanged phenols or naphthols, and to still further improve thestability towards light of the vulcanizates obtained from our products.In general, an amount of up to about 3% of our condensation products,either hydrogenated or non-hydrogenated (calculated upon the amount ofthe synthetic-rubber) is suflicient to exert the desired result.

Our new auxiliary products are not only suitable stabilizing agents forthe said synthetic rubber-like materials. They are also capable ofexerting a favorable influence upon the course of the oxidizingtreatment which is described and' claimed in the prior application Ser.No. 196,903 to Albert Koch and Erich Gartner filed March 19, 1938, andserves to effect a further improvement of the plasticity of polymericbutadiene hydrocarbons obtained according to the emulsion polymerizationprocess, and also of the mixed emulsion polymerizates of butadienehydrocarbons and activated vinyl compounds such as styrene. It is to beunderstood that our new stabilizing agents fall within the scope of thetermfanti-oxidants as used in the said application Ser. No. 196,903.

Suitable aldehydes or ketones for preparing our stabilizing agents areformaldehyde, acetaldehyde, benzaldehyde, acetone cyclohexanone and thelike, whereas the phenols and naphthols may contain various substituentssuch as alkyls or halogens.

The following examples illustrate the inven tion without beingrestricted thereto, the parts being by weight.

EXAMPLE 1 51 parts of a condensation product prepared by causing 12parts of a 30% formaldehyde solution to react with 25 parts of a crudecresol in the presence of 0.5 part of concentrated hydrochloric acid at70 C., separating the resin from the water and removing the excesscresol by evaporation at 180 C. and 18 mm. pressure, are dissolved inthe necessary amount of a n-caustic soda lye and then incorporated whilestirring within an aqueous emulsion of 1700 parts of a mixedpolymerizate of 75 per cent of butadiene and 25 per cent of acrylic acidnitrile prepared as described in Patent No. 1,973,000 to Erich Konradand Eduard Tschunkur. Thereupon coagulation of the emulsion is effectedby acidification by means of acetic acid followed by the addition of asaturated sodium chloride solution.

In the following tables the properties of the resulting solid productare defined in figures indicating the plasticity of the crudeunvulcanized product, on an unvulcanized rubber mixture preparedtherefrom, and the mechanical properties of the vulcanizates preparedfrom the said mixture. The plasticity (A) has been defined by measuringthe strength in grams which is necessary for compressing within 30seconds a mm. high cylinder of the material to be tested to a height of4 mm. The symbols (B) (C) (D), and (E) indicate the tensile strength (inkg. per square centimeter), the elongation and the elasticity in percent and the hardness of the vulcanizate (in degree Shore.)

In the following tables (a) shows the properties of the productstabilized as defined above, whereas in case of the symbols (b) and (c)the above condensationlproduct has been replaced by an equal amount ofthe uniform products R.CH2.R and R.CH2.R.CH=.R, R being the radicle ofp-cresol.

Table I shows the plasticity of the unvulcanized crude product and theplasticity of an unvulcanized mixture and the mechanical properties ofthe vulcanizates obtained therefrom, the

composition of the mixture being as follows:

Table II gives the mechanical properties of vulcanizates of a mixture ofthe following composition:

Parts Above stabilized product Zinc oxide 10 Titanium dioxide 20 Sulfur1 Accelerator 1 Table III shows the gradual increase in plasticity whichis observed upon subjecting the stabilized synthetic rubber to anoxidizing treatment in the heat in accordance with application Ser. No.196,993.

Tablei C d .B C D E ru e product Mixture B O D E ((1).. 113 640 49 64Eb) 131 660 50 64 c 121 630 49 64 Table III Timeinminutes a b 0 EXAMPLE2 conjoint polymerization of 75% of butadiene and 25% of styrene. Thesynthetic rubber is isolated as described in Example 1. Table IV showsthe figures obtained from this product, the composition of the mixturefor vulcanization corresponding to that of Table I:

Table IV.

B c D -E Crude Unvulcenized product mixture The next table correspondsto Table III in that it shows the efiect of the oxidizing treatment of.

the process of application Ser. No. 196,903.

- Table V Time in minutes Plasticity n 3,700 so 650 to 400Simiiarresults have been obtained with the following products:

EXAMPLE 3 35 parts of a condensation product which has been obtained asdescribed in Example 1 from crude cresol and formaldehyde'in the molarproportion of 2:1 and has been subsequently sub- Jected to ahydrogenating process until it has taken up 13% of the amount ofhydrogen which would be necessary for hydrogenating every aromaticnucleus contained therein, are suspended in 200 parts of a. 4.2% aqueoussolution of sodium isobutylnaphthalene sulfonic acid by means of amixer. The suspension is incorporated while stirring within an emulsionof 1260 parts of the synthetic rubber as described in Example 2.Precipitation is effected as described in Example 1. Theresultingproduct has proved to be excellently stable on storing and iscapable of being quickly plasticized if subjected to the oxidizingtreatment as described in application Ser. No. 196,903. The unvulcanizedproduct as well as the vulcanizates thereof are free from anydisagreeable odor and are stable towards light.

The following table shows the improvement in plasticity obtained uponsubjecting the stabilized product to the oxidizing treatment asdescribed in application Ser. No. 196,903:

Table VI I Time in minutes droxy compound selected from the groupconsisting of phenols and naphthols with an organic carbonyl compoundselected from the group consisting of aldehydes and ketones, thesecondensation products being soluble in organic solvents, and effectingprecipitation of the said latex.

2. The process as claimed in claim 1 wherein as condensation productthere is employed a product of the reaction of cresol and formaldehyde.

3. The process as claimed in claim 1 wherein such condensation productsof the character described are employed as have been hydrogenated to adegree at which at the most 50 per cent of the amount of hydrogen hasbeen taken up which is necessary for efiecting complete hydrogenation ofthe aromatic nuclei contained therein.

HANS MURKE. WILHELM BECKER.

Plasticity n

